In the 3rd Generation Partnership Project (3GPP) standardization body technologies like Global System for Mobile Communication (GSM), High-Speed Packet Access (HSPA) and Long Term Evolution (LTE) have been and are currently developed.
LTE is the latest technology standardised. It uses an access technology based on Orthogonal Frequency Division Multiplexing (OFDM) for the downlink (DL) and Single Carrier FDMA (SC-FDMA) for the uplink (UL). The resource allocation to mobile stations, in LTE denoted user equipment (UE), on both DL and UL is performed adaptively by the concept of fast scheduling, taking into account the instantaneous traffic pattern and radio propagation characteristics of each UE. Assigning resources in both DL and UL is performed in a so-called scheduler situated in a base station, in LTE often denoted eNodeB. As illustrated in FIG. 1, LTE transmissions are sent from base stations 102, in a telecommunications network 104, to UEs 106, 108.
As illustrated in FIG. 2, a sub-frame 200 may be transmitted in accordance with the LTE standard, and may consist of 12 or 14 sub-carriers 204 in the frequency domain. In the time domain, the sub-frame may be divided into a number of OFDM (or SC-FDMA) symbols 208. An OFDM (or SC-FDMA) symbol 208 may include a cyclic prefix 206. A unit of one sub-carrier and one symbol is referred to as a resource element (RE) 202. Thus, a sub-frame may consist of, for example, 84 REs in a 12×7 configuration as shown in FIG. 2.
In e.g. LTE, uplink transmissions are scheduled by a base station. A grant is transmitted on the Physical Downlink Control Channel (PDCCH) and the UE responds with a transmission using the resources specified in the grant and with the size specified in the grant. The UE can let the base station know that it wants to transmit by sending a scheduling request (SR) on the Physical Uplink Control Channel (PUCCH) at predefined times. Typically the UE transmits an SR which is followed by one or many grants, each resulting in one uplink transmission. This is commonly referred to as dynamic scheduling.
With the higher speeds a number of various applications that a user of the UE can be engaged in have evolved. It is for instance of interest for a user to involve him- or herself in online games, where small amounts of uplink data are transferred fairly often from the UE to another device involved in a game. Here the transferred data may be gaming commands and the other device may be another UE or another type of user terminal like a PC or even a server. Gaming is one example of delay-sensitive traffic. The increase of this delay-sensitive traffic and its significant share in the Internet traffic leads to the radio interfaces of wireless communication systems having to meet various latency requirements to ensure that a UE user can enjoy the activities employing this type of traffic. Another example of delay-sensitive traffic is ping. Ping is for instance used to estimate the delay of a channel as well as to measure the performance in radio systems in order to for instance compare and/or rank different systems.
Setting up of traffic in a wireless communication network is often referred as allocation of resources. When resources are allocated to a UE desiring to send data in the uplink, there are normally a number of activities that have to be performed. First the UE sends a scheduling request (SR) informing the base station that the UE has an unspecified amount of data to send. This is followed by the base station responding with a grant, which grant includes information on what time/frequency resources the UE shall use. The UE then transfers a Buffer Status Report (BSR) informing the base station that the amount of data the UE intends to send is within a predefined range. The amount of data available is specified for logical channel groups rather than individual bearers. After receiving the BSR the base station issues a grant for further data. It is not until it receives this further grant that the UE can transmit the actual data it intends. This process is time consuming, especially if the UE is to run through the process each time it desires to transfer data.
Instead of dynamic scheduling, semi-persistent scheduling (SPS) can be used. The purpose with SPS is to save resources on the PDCCH when it is known beforehand when data will arrive to the UE. When SPS is used, a semi-persistent scheduling interval is signalled to the UE through the RRC protocol. Special grants (SPS grants/semi-persistent scheduling uplink grants) are then used to configure a recurring grant with the specified interval. One grant can hence be used for multiple transmissions. The semi-persistent grant is valid until it is cancelled by a special grant that explicitly releases the semi-persistent grant. To optimize the power saving with SPS, a mechanism has been added so that no SR is triggered by specified logical channels while an SPS grant is configured.
It is not required that an SR precedes the grant. When the base station knows that a UE has a periodic service or for some other reason can predict future data arrivals it can transmit a grant to the UE without waiting for an SR. It is also possible to blindly transmit grants in order to speed up the scheduling and hence reduce the delay. These scheduling methods are called predictive scheduling and the grants are transmitted from the base station to the UE on the downlink control channel, e.g. PDCCH.
WO2012/148331 discloses a method applying predictive scheduling. Upon receipt of a service indicator from a UE the base station determines an uplink transmission scheme for the UE based on the service indicator. Uplink prescheduling according to the prior art may however result in waste of system resources in case the UE has nothing to send and replies to the prescheduling grants including an empty BSR and padding. Therefore predictive scheduling may lead to a waste of resource and is thus restricted to situations when the traffic load is below certain threshold values so that it will not conflict with regular scheduling in higher traffic load situations.